JP-A 57-118512 discloses a process for producing sustained-release microcapsules of a water-soluble drug which comprises encapsulating the drug by coacervation phase separation. This process has the following disadvantages: (1) the water-soluble drug is leaked out to the outer aqueous phase, and the drug entrapment ratio decreases, and it is difficult to obtain microcapsules having a high drug content, and (2) the resulting microcapsules have many pores and cause a large initial drug release. Journal of Pharmaceutical Science Vol. 75, No. 8, p. 750-755 (1986) discloses a process for producing microspheres which comprises preparing an s/o/w type emulsion from a dispersion of micronized dry powder of cisplatin in a poly(dl-lactide) solution and subjecting the emulsion to an in-water drying process. However, this literature fails to teach or suggest amorphous cisplatin or sustained-release of the drug over a long period.